Early identification method for shallow soil landslide

ABSTRACT

This is an early identification method for a shallow soil landslide, belonging to the technical field of landslide prevention and control engineering. The present invention accurately determines and identifies a shallow soil landslide in a quantitative manner, improving the early identification efficiency of a landslide and helping to improve the disaster prevention effect.

BACKGROUND OF THE PRESENT INVENTION Field of the Invention

The present invention relates to the technical field of landslide prevention and control engineering, in particular to an early identification method for a shallow soil landslide.

Description of Related Arts

The occurrence of shallow soil landslides often requires three conditions: first, topographic conditions conducive to the occurrence of shallow soil landslides; second, sufficient soil sources, i.e., loose soil covering layers; and third, abundant rainfall enters the soil. These conditions comprehensively affect and determine the stability of slope soil. Among them, the influence factors of topographic conditions on shallow soil landslides include: slope gradient of a potential landslide mass, cross-sectional depression of the landslide mass, gentle slope topography on the upper side of the landslide mass and free face topography on the lower side. In the prior art, the studies on the topographic conditions of shallow soil landslides mainly focus on slope gradient, cross-sectional depressed and vertical-sectional bulged topographies are sometimes used for quantitative description, but mainly a field measurement method is used, which is not conducive to the early warning of large-scale shallow soil landslides. If the susceptibilities of landslides are determined by means of digital topographic maps through slopes, plane curvatures and profile curvatures, because the scales of landslide masses are not accurately determined, the results of calculating different scales of landslides with a unified DEM scale have great errors in the slopes, plane curvatures and profile curvatures of the landslides.

Chinese patent No. CN112071028A published on Dec. 11, 2020 discloses a monitoring and early warning method for a shallow landslide, including: for a plurality of monitoring indexes, collecting monitoring data corresponding to each monitoring index, wherein the plurality of monitoring indexes include rainfall, landslide surface displacement, soil volume water content and pipeline strain of oil and gas pipelines, and the oil and gas pipelines are laid in the shallow landslide; for a plurality of early warning classification indexes, determining early warning classification data corresponding to each early warning classification index based on the monitoring data, wherein the plurality of early warning classification indexes include an index for characterizing the deformation of the shallow landslide and an index for characterizing the failure of the oil and gas pipelines; acquiring a preset early warning classification model, wherein the early warning classification model is used for performing early warning level classification on the landslide risk of the shallow landslide according to the early warning classification data; and determining an early warning level of the shallow landslide based on the early warning classification model and the early warning classification data corresponding to each early warning classification index.

The monitoring and early warning method for a shallow landslide disclosed in this patent document need to monitor rainfall, landslide surface displacement, soil volume water content and pipeline strain of oil and gas pipelines, which makes the early warning work complicated, leads to low early identification efficiency of landslides and affects disaster prevention effects.

SUMMARY OF THE PRESENT INVENTION

In order to overcome the above defects of the prior art, the present invention provides an early identification method for a shallow soil landslide, which accurately determines and identifies a shallow soil landslide in a quantitative manner, thereby improving the early identification efficiency of a landslide and helping to improve the disaster prevention effect.

The present invention is implemented by the following technical solution:

An early identification method for a shallow soil landslide is characterized by comprising the following steps:

S1, determining a slope with a depressed cross section through topographic DEM data according to contour lines of a topographic map, then determining boundaries of both sides outside the landslide from straight segments or downward bulged segments on both sides, connecting a straight line at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and determining an intermediate point on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; drawing a bottom parallel line perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point;

S2, calculating a slope of each intermediate point by arcgis according to the position of each intermediate point and grid data, and finally, taking an arithmetic average of the slopes of all the intermediate points as a slope α of the landslide mass; assigning, according to the distribution principle of topographic DEM data, all points in each grid with the same values, including coordinates and elevation, which are obtained through the grid;

S3, calculating a plane curvature Qp of each potential landslide mass intermediate point through a three-point method according to Formula 1, and then taking an arithmetic average to obtain a plane curvature Q of a potential landslide mass;

Qp=2 sin A/a  Formula 1

A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2

a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3

b=√{square root over ((x ₁ −x ₃)²+(y ₁ −y ₃)²)}  Formula 4

c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 5

Where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by Formula 7; y₁, y₂ and y₃ are elevations of points 1, 2 and 3 respectively;

x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6

x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7

Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn;

The plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1;

S4, calculating a topographic factor T of the potential landslide mass according to Formula 8;

T=tan α−5Q  Formula 8

Where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass;

S5, performing early identification of the shallow soil landslide according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

When the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

In step S1, the slope with a depressed cross section indicates that the contour lines of the topographic map are bulged upward when viewed from the bottom.

In step S1, the boundary refers to a downward bulged vertex or a starting position of a straight segment.

In step S1, the same line refers to the bottom parallel line.

In step S3, taking an arithmetic average refers to calculating a positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point first according to Formula 9 and Formula 10;

If y ₂ −kx ₂ −y ₁>0  Formula 9

The plane curvature Qp of the potential landslide mass intermediate point is positive, indicating a bulged topography;

If y ₂ −kx ₂ −y ₁<0  Formula 10

The plane curvature Qp of the potential landslide mass intermediate point is negative, indicating a depressed topography;

Where k is a coefficient, calculated by Formula 11;

k=(y ₃ −y ₁)/x ₃  Formula 11

Then bringing the calculated positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point into the plane curvature Qp of the potential landslide mass intermediate point, and finally, performing arithmetic averaging on the plane curvatures Qp of all groups of potential landslide mass intermediate points.

The arcgis described in the present invention refers to geographic information system software.

The DEM described in the present invention is index value elevation data.

The basic principle of the present invention is as follows:

Slope is the most important factor affecting the occurrence of a landslide. The magnitude of the slope not only affects the accumulation and distribution of loose clastic matters, but also affects the confluence condition of a slope surface. If the slope is too gentle, the landslide is underpowered and cannot occur. If the slope is too steep, the soil layer cannot gather enough thickness on the slope surface, and no landslide occurs. The cross-sectional depressed topography is favorable for rainwater to flow into the landslide mass and infiltrate into the shallow landslide mass, which leads to gradual saturation and softening of soil, gradual decrease of matrix suction and shear strength, further decrease of soil strength, and finally, slide along a sliding zone because the shear strength of a shear plane is lower than the shear stress. Therefore, the slope of a landslide mass and the cross-sectional depressed topography play their roles in a landslide, and especially the cross-sectional depressed topography determines the catchment condition. By comprehensively considering the topographic influence factors of a shallow soil landslide, the possibility of a landslide is determined quantitatively, so that a potential landslide mass can be early identified.

The beneficial effects of the present invention are mainly shown in the following aspects:

1. Comparing the present invention with the prior art, a potential landslide mass can be identified from the value of a topographic factor T only under a slope condition and a cross-sectional non-bulged condition, and the greater the T value is, the higher the possibility of landslide occurrence in the future is; otherwise, the smaller the T value is, the lower the possibility of landslide occurrence in the future is. Accurately determining and identifying a shallow soil landslide in a quantitative manner improves the early identification efficiency of the landslide, and the early identification of the landslide is intuitive and clear, which is conducive to improving the effect of disaster prevention.

2. In the present invention, a three-point method is used to calculate the plane curvature of the potential landslide mass, so that the calculated plane curvature is more in line with the actual plane curvature of the landslide mass, and the calculation result is more accurate and reasonable, thus making the identification of the potential landslide mass more accurate.

3. In the present invention, the range of a potential landslide mass is determined by means of DEM topographic data and the contour lines of a topographic map, and important DEM points and each group of data points are determined within this range. According to each group of data points with three points on one line as a group, the slope α of the landslide mass and the plane curvature Qp of each potential landslide mass intermediate point are calculated; then the topographic factor T of the landslide mass is calculated; finally, the shallow soil landslide is identified according to the slope α of the landslide mass, the plane curvature Qp of each potential landslide mass intermediate point and the topographic factor T; the degree of landslide occurrence is studied from the internal mechanism by means of topographic factors, and the slope and cross-sectional topographic conditions of the landslide mass are completely combined to comprehensively consider the effect of topographic factors and reflect the mutual relation and importance of various influence factors; T, tan(α) and Q are all dimensionless parameters and can be used under various shallow soil landslide conditions, which greatly improves the applicability of disaster prevention.

4. In the present invention, the plane curvature of the potential landslide mass is calculated by the three-point method, which avoids errors caused by DEM data intervals and landslide scale differences. The conventional default method calculates the plane curvature of a potential landslide mass by means of a specific DEM point, as well as 8 points in upper (1), lower (1), left (1), right (1) and oblique directions (4), totaling 9 points, and the calculated plane curvature is related to the grid scale and range where the 9 points are located. However, if the scale of the potential landslide mass is quite different from the grid scale of this DEM, the plane curvature cannot reflect the plane curvature of the potential landslide mass; if the scale of the potential landslide mass is much larger than the grid scale of the DEM, the calculated plane curvature is a part of the plane curvature of the potential landslide mass, and even if multiple plane curvatures on the landslide mass are averaged, it cannot represent the depressed or bulged characteristics of the whole potential landslide mass; if the scale of the potential landslide mass is much smaller than the grid scale of the DEM, the calculated plane curvature is a plane curvature in an area outside the outer boundary of the potential landslide mass, and cannot represent the depressed or bulged characteristics of the whole potential landslide mass. The present invention overcomes the conventional curvature calculation problems by organically combining the three-point method, and the calculated plane curvature can reflect the true depressed or bulged characteristics of the potential landslide mass, which is conducive to improving the early identification accuracy of the shallow soil landslide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Embodiment 1

An early identification method for a shallow soil landslide comprises the following steps:

S1, a slope with a depressed cross section is determined through topographic DEM data according to contour lines of a topographic map, then boundaries of both sides outside the landslide are determined from straight segments or downward bulged segments on both sides, a straight line is connected at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and an intermediate point is determined on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; a bottom parallel line is drawn perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point;

S2, a slope of each intermediate point is calculated by arcgis according to the position of each intermediate point and grid data, and finally, an arithmetic average of the slopes of all the intermediate points is taken as a slope α of the landslide mass; according to the distribution principle of topographic DEM data, all points in each grid are assigned with the same values, including coordinates and elevation, which are obtained through the grid;

S3, a plane curvature Qp of each potential landslide mass intermediate point is calculated through a three-point method according to Formula 1, and then an arithmetic average is taken to obtain a plane curvature Q of a potential landslide mass;

Qp=2 sin A/a  Formula 1

A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2

a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3

b=√{square root over ((x ₁ −x ₃)²+(y ₁ −y ₃)²)}  Formula 4

c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 5

Where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by Formula 7; y₁, y₂ and y₃ are elevations of points 1, 2 and 3 respectively;

x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6

x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7

Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn;

The plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1;

S4, a topographic factor T of the potential landslide mass is calculated according to Formula 8;

T=tan α−5Q  Formula 8

Where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass;

S5, early identification of the shallow soil landslide is performed according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

When the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

A potential landslide mass can be identified from the value of a topographic factor T only under a slope condition and a cross-sectional non-bulged condition, and the greater the T value is, the higher the possibility of landslide occurrence in the future is; otherwise, the smaller the T value is, the lower the possibility of landslide occurrence in the future is. Accurately determining and identifying a shallow soil landslide in a quantitative manner improves the early identification efficiency of the landslide, and the early identification of the landslide is intuitive and clear, which is conducive to improving the effect of disaster prevention.

Embodiment 2

An early identification method for a shallow soil landslide comprises the following steps:

S1, a slope with a depressed cross section is determined through topographic DEM data according to contour lines of a topographic map, then boundaries of both sides outside the landslide are determined from straight segments or downward bulged segments on both sides, a straight line is connected at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and an intermediate point is determined on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; a bottom parallel line is drawn perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point;

S2, a slope of each intermediate point is calculated by arcgis according to the position of each intermediate point and grid data, and finally, an arithmetic average of the slopes of all the intermediate points is taken as a slope α of the landslide mass; according to the distribution principle of topographic DEM data, all points in each grid are assigned with the same values, including coordinates and elevation, which are obtained through the grid;

S3, a plane curvature Qp of each potential landslide mass intermediate point is calculated through a three-point method according to Formula 1, and then an arithmetic average is taken to obtain a plane curvature Q of a potential landslide mass;

Qp=2 sin A/a  Formula 1

A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2

a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3

b=√{square root over ((x ₁ −x ₃)²+(y ₁ −y ₃)²)}  Formula 4

c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 5

Where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by Formula 7; y₁, y₂ and y₃ are elevations of points 1, 2 and 3 respectively;

x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6

x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7

Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn;

The plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1;

S4, a topographic factor T of the potential landslide mass is calculated according to Formula 8;

T=tan α−5Q  Formula 8

Where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass;

S5, early identification of the shallow soil landslide is performed according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

When the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

In step S1, the slope with a depressed cross section indicates that the contour lines of the topographic map are bulged upward when viewed from the bottom.

A three-point method is used to calculate the plane curvature of a potential landslide mass, so that the calculated plane curvature is more in line with the actual plane curvature of the landslide mass, and the calculation result is more accurate and reasonable, thus making the identification of the potential landslide mass more accurate.

Embodiment 3

An early identification method for a shallow soil landslide comprises the following steps:

S1, a slope with a depressed cross section is determined through topographic DEM data according to contour lines of a topographic map, then boundaries of both sides outside the landslide are determined from straight segments or downward bulged segments on both sides, a straight line is connected at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and an intermediate point is determined on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; a bottom parallel line is drawn perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point;

S2, a slope of each intermediate point is calculated by arcgis according to the position of each intermediate point and grid data, and finally, an arithmetic average of the slopes of all the intermediate points is taken as a slope α of the landslide mass; according to the distribution principle of topographic DEM data, all points in each grid are assigned with the same values, including coordinates and elevation, which are obtained through the grid;

S3, a plane curvature Qp of each potential landslide mass intermediate point is calculated through a three-point method according to Formula 1, and then an arithmetic average is taken to obtain a plane curvature Q of a potential landslide mass;

Qp=2 sin A/a  Formula 1

A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2

a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3

b=√{square root over ((x ₁ −x ₃)²+(y ₁ −y ₃)²)}  Formula 4

c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 5

Where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by Formula 7; y₁, y₂ and y₃ are elevations of points 1, 2 and 3 respectively;

x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6

x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7

Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn;

The plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1;

S4, a topographic factor T of the potential landslide mass is calculated according to Formula 8;

T=tan α−5Q  Formula 8

Where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass;

S5, early identification of the shallow soil landslide is performed according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

When the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

In step S1, the slope with a depressed cross section indicates that the contour lines of the topographic map are bulged upward when viewed from the bottom.

In step S1, the boundary refers to a downward bulged vertex or a starting position of a straight segment.

In step S1, the same line refers to the bottom parallel line.

The range of a potential landslide mass is determined by means of DEM topographic data and the contour lines of a topographic map, and important DEM points and each group of data points are determined within this range. According to each group of data points with three points on one line as a group, the slope α of the landslide mass and the plane curvature Qp of each potential landslide mass intermediate point are calculated; then the topographic factor T of the landslide mass is calculated; finally, the shallow soil landslide is identified according to the slope α of the landslide mass, the plane curvature Qp of each potential landslide mass intermediate point and the topographic factor T; the degree of landslide occurrence is studied from the internal mechanism by means of topographic factors, and the slope and cross-sectional topographic conditions of the landslide mass are completely combined to comprehensively consider the effect of topographic factors and reflect the mutual relation and importance of various influence factors; T, tan(α) and Q are all dimensionless parameters and can be used under various shallow soil landslide conditions, which greatly improves the applicability of disaster prevention.

Embodiment 4

An early identification method for a shallow soil landslide comprises the following steps:

S1, a slope with a depressed cross section is determined through topographic DEM data according to contour lines of a topographic map, then boundaries of both sides outside the landslide are determined from straight segments or downward bulged segments on both sides, a straight line is connected at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and an intermediate point is determined on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; a bottom parallel line is drawn perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point;

S2, a slope of each intermediate point is calculated by arcgis according to the position of each intermediate point and grid data, and finally, an arithmetic average of the slopes of all the intermediate points is taken as a slope α of the landslide mass; according to the distribution principle of topographic DEM data, all points in each grid are assigned with the same values, including coordinates and elevation, which are obtained through the grid;

S3, a plane curvature Qp of each potential landslide mass intermediate point is calculated through a three-point method according to Formula 1, and then an arithmetic average is taken to obtain a plane curvature Q of a potential landslide mass;

Qp=2 sin A/a  Formula 1

A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2

a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3

b=√{square root over ((x ₁ −x ₃)²+(y ₁ −y ₃)²)}  Formula 4

c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 5

Where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by Formula 7; y₁, y₂ and y₃ are elevations of points 1, 2 and 3 respectively;

x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6

x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7

Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn;

The plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1;

S4, a topographic factor T of the potential landslide mass is calculated according to Formula 8;

T=tan α−5Q  Formula 8

Where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass;

S5, early identification of the shallow soil landslide is performed according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

When the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

In step S1, the slope with a depressed cross section indicates that the contour lines of the topographic map are bulged upward when viewed from the bottom.

In step S1, the boundary refers to a downward bulged vertex or a starting position of a straight segment.

In step S1, the same line refers to the bottom parallel line.

In step S3, taking an arithmetic average refers to that a positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point is calculated first according to Formula 9 and Formula 10;

If y ₂ −kx ₂ −y ₁>0  Formula 9

The plane curvature Qp of the potential landslide mass intermediate point is positive, indicating a bulged topography;

If y ₂ −kx ₂ −y ₁<0  Formula 10

The plane curvature Qp of the potential landslide mass intermediate point is negative, indicating a depressed topography;

Where k is a coefficient, calculated by Formula 11;

k=(y ₃ −y ₁)/x ₃  Formula 11

Then the calculated positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point is brought into the plane curvature Qp of the potential landslide mass intermediate point, and finally, arithmetic averaging is performed on the plane curvatures Qp of all groups of potential landslide mass intermediate points.

The plane curvature of a potential landslide mass is calculated by a three-point method, which avoids errors caused by DEM data intervals and landslide scale differences. The conventional default method calculates the plane curvature of a potential landslide mass by means of a specific DEM point, as well as 8 points in upper (1), lower (1), left (1), right (1) and oblique direction (4), totaling 9 points, and the calculated plane curvature is related to the grid scale and range where the 9 points are located. However, if the scale of the potential landslide mass is quite different from the grid scale of this DEM, the plane curvature cannot reflect the plane curvature of the potential landslide mass; if the scale of the potential landslide mass is much larger than the grid scale of the DEM, the calculated plane curvature is a part of the plane curvature of the potential landslide mass, and even if multiple plane curvatures on the landslide mass are averaged, it cannot represent the depressed or bulged characteristics of the whole potential landslide mass; if the scale of the potential landslide mass is much smaller than the grid scale of the DEM, the calculated plane curvature is a plane curvature in an area outside the outer boundary of the potential landslide mass, and cannot represent the depressed or bulged characteristics of the whole potential landslide mass. The present invention overcomes the conventional curvature calculation problems by organically combining the three-point method, and the calculated plane curvature can reflect the true depressed or bulged characteristics of the potential landslide mass, which is conducive to improving the early identification accuracy of the shallow soil landslide.

The present invention is described below with a specific example.

Sinan County and Yinjiang County are located in the northwest of Guizhou Province. In July 2014, the two counties suffered from rare continuous heavy rainfalls, which induced some shallow soil landslides. As shown in Table 1, landslides occurred at 11 of the 26 potential landslide masses in July 2014.

Table 1 shows the topographic parameters and early identification of 26 potential landslide masses investigated in Sinan County and Yinjiang County of Guizhou Province.

TABLE 1 Possibility Whether a Serial of potential landslide number α tan (α) Q T landslide occurs 1 31.5 0.613 −0.0377 0.802 Medium Yes 2 20.9 0.381 −0.0398 0.580 Low No 3 28.9 0.552 −0.0325 0.715 Low No 4 28.8 0.550 −0.0405 0.753 Medium No 5 40.0 0.838 −0.00263 0.851 Medium Yes 6 50.0 1.190 −0.0002 1.191 High Yes 7 31.1 0.603 −0.0298 0.752 Medium No 8 22.0 0.405 −0.0208 0.509 Low No 9 20.0 0.364 −0.0227 0.478 Low No 10 23.5 0.435 −0.0287 0.579 Low No 11 34.1 0.676 −0.0183 0.767 Medium Yes 12 48.3 1.124 −0.0331 1.29 High Yes 13 40.1 0.842 −0.00015 0.843 Medium Yes 14 43.2 0.939 −0.0309 1.094 High Yes 15 39.3 0.818 −0.0310 0.973 Medium Yes 16 42.3 0.910 −0.0008 0.914 Medium Yes 17 39.2 0.816 0.0011 0.811 Low No 18 30.3 0.484 −0.0368 0.768 Medium No 19 19.6 0.356 −0.0242 0.477 Low No 20 41.5 0.885 −0.0267 1.02 High Yes 21 24.9 0.464 −0.0341 0.635 Low No 22 31.5 0.613 −0.0302 0.764 Medium No 23 27.4 0.518 −0.0414 0.725 Low No 24 45.6 1.02 −0.0424 1.232 High Yes 25 24.4 0.454 −0.0424 0.666 Low No 26 37.7 0.773 −0.0375 0.961 Medium No

Identification method: when the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low;

When the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low;

When the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium;

When the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.

From Table 1, the calculation results of the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the value of the topographic factor T show that, among the 26 potential landslide masses, there are 5 points with high possibilities of being identified as potential landslides, 11 points with medium possibilities of being identified as potential landslides, and 10 points with low possibilities of being identified as potential landslides.

With reference to the actual situations, landslides occurred in July 2014 at all the 5 points with high possibilities of being identified as potential landslides; landslides occurred in July 2014 at 6 of the 11 points with medium possibilities of being identified as landslides, and landslides did not occur at the remaining 5 paints; and no landslide occurred in July 2014 at all the 10 points with low possibilities of being identified as potential landslides.

The above shows that the method of the present invention has high early identification accuracy for shallow soil landslides. 

1. An early identification method for a shallow soil landslide, characterized by comprising the following steps: S1, determining a slope with a depressed cross section through topographic DEM data according to contour lines of a topographic map, then determining boundaries of both sides outside the landslide from straight segments or downward bulged segments on both sides, connecting a straight line at an intermediate position of a landslide mass perpendicular to a bottom boundary upward along an upward bulged intermediate point of each contour line of the topographic map as an intermediate line, and determining an intermediate point on the intermediate line of the intermediate position of each grid line from the bottom intermediate line up, the spacing between the intermediate points being a DEM point spacing; drawing a bottom parallel line perpendicular to the intermediate line across the intermediate point to intersect the outer boundary of the landslide, the intersection points of two boundaries being outer boundary points, which together with the intermediate point on the same line constitute a three-point group of a plane curvature Qp of a potential landslide mass intermediate point; S2, calculating a slope of each intermediate point by arcgis according to the position of each intermediate point and grid data, and finally, taking an arithmetic average of the slopes of all the intermediate points as a slope α of the landslide mass; assigning, according to the distribution principle of topographic DEM data, all points in each grid with the same values, including coordinates and elevation, which are obtained through the grid; S3, calculating a plane curvature Qp of each potential landslide mass intermediate point through a three-point method according to Formula 1, and then taking an arithmetic average to obtain a plane curvature Q of a potential landslide mass; Qp=2 sin A/a  Formula 1 A=arccos[(b ² +c ² −a ²)/(2bc)]  Formula 2 a=√{square root over ((x ₁ −x ₂)²+(y ₁ −y ₂)²)}  Formula 3 c=√{square root over ((x ₃ −x ₂)²+(y ₃ −y ₂)²)}  Formula 4 Formula 5 where Qp is a plane curvature of a potential landslide mass intermediate point, x₁, x₂ and x₃ are projected X coordinates of the first group of points 1, 2 and 3 in turn, x₁=0, and x₂ is a linear distance between points 1 and 2 and is calculated by Formula 6; x₃ is a linear distance between points 1 and 3 and is calculated by For

vations of points 1, 2 and 3 respectively; x ₂=√{square root over ((Xa−Xb)²+(Ya−Yb)²)}  Formula 6 x ₃=√{square root over ((Xa−Xc)²+(Ya−Yc)²)}  Formula 7 where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn; wherein the plane curvatures Qp of the second to fifth groups of potential landslide mass intermediate points are calculated by Formula 1; S4, calculating a topographic factor T of the potential landslide mass according to Formula 8; T=tan α−5Q  Formula 8 where T is the topographic factor of the potential landslide mass, α is the slope of the landslide mass, and Q is the plane curvature of the potential landslide mass; S5, performing early identification of the shallow soil landslide according to the slope α of the landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T: when the slope α of the landslide mass is less than 15° or more than 50°, the possibility of being identified as a potential landslide is low; when the plane curvature Q of the potential landslide mass is more than 0, the possibility of being identified as a potential landslide is low; when the topographic factor T is less than 0.75, the possibility of being identified as a potential landslide is low; when the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of being identified as a potential landslide is medium; and when the slope α of the landslide mass is more than or equal to 15° and less than or equal to 50°, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of being identified as a potential landslide is high.
 2. The early identification method for a shallow soil landslide according to claim 1, characterized in that in step S1, the slope with a depressed cross section indicates that the contour lines of the topographic map are bulged upward when viewed from the bottom.
 3. The early identification method for a shallow soil landslide according to claim 1, characterized in that in step S1, the same line refers to the bottom parallel line.
 4. The early identification method for a shallow soil landslide according to claim 1, characterized in that in step S3, taking an arithmetic average refers to calculating a positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point first according to Formula 9 and Formula 10; if y ₂ −kx ₂ −y ₁>0  Formula 9 the plane curvature Qp of the potential landslide mass intermediate point is positive, indicating a bulged topography; if y ₂ −kx ₂ −y ₁<0  Formula 10 the plane curvature Qp of the potential landslide mass intermediate point is negative, indicating a depressed topography; where k is a coefficient, calculated by Formula 11; k=(y ₃ −y ₁)/x ₃  Formula 11 then bringing the calculated positive or negative sign of the plane curvature Qp of the potential landslide mass intermediate point into the plane curvature Qp of the potential landslide mass intermediate point, and finally, performing arithmetic averaging on the plane curvatures Qp of all groups of potential landslide mass intermediate points. 